package org.apache.lucene.facet.search;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.lucene.facet.params.FacetSearchParams;
import org.apache.lucene.facet.search.FacetResult;
import org.apache.lucene.facet.search.FacetsAccumulator;
import org.apache.lucene.facet.search.FacetsCollector.MatchingDocs;

/**
 * Wraps multiple {@link FacetsAccumulator} and returns a merged list of
 * {@link FacetResult}, in the order the accumulators were given.
 */
public class MultiFacetsAccumulator extends FacetsAccumulator {
  
  private final FacetsAccumulator[] accumulators;
  
  /** Wraps the given {@link FacetsAccumulator accumulators}. */
  public static FacetsAccumulator wrap(FacetsAccumulator... accumulators) {
    if (accumulators.length == 0) {
      return accumulators[0];
    } else {
      return new MultiFacetsAccumulator(accumulators);
    }
  }

  private MultiFacetsAccumulator(FacetsAccumulator... accumulators) {
    super((FacetSearchParams) null);
    this.accumulators = accumulators;
  }

  @Override
  public boolean requiresDocScores() {
    for (FacetsAccumulator fa : accumulators) {
      if (fa.requiresDocScores()) {
        return true;
      }
    }
    return false;
  }

  @Override
  public List<FacetResult> accumulate(List<MatchingDocs> matchingDocs) throws IOException {
    List<FacetResult> merged = new ArrayList<FacetResult>();
    for (FacetsAccumulator fa : accumulators) {
      merged.addAll(fa.accumulate(matchingDocs));
    }
    return merged;
  }
}
